(1) Field to Which Invention Relates
The invention relates to a heart frequency measuring instrument with a frequency measuring device to be carried on the arm, with a cable connecting the measuring instrument with measuring electrodes carried on the body and with an optical display for the measured heart frequency.
(2) The Prior Art
Such a heart frequency measuring instrument or cardiotachometer is described for example in the German Patent Specification (Offenlegungsschrift) No. 2,309,467 and comprises an analog computer accommodated in the housing, which is connected with two electrodes fixed to the thorax of the patient, calculates the heart frequency in heart beats per minute and displaces the calculated value on a tacho instrument with a scale. The device described in this case is however subject to a whole series of disadvantages. On the one hand the computer connected with a 9 volt battery voltage is an analog computer, which generally has a substantial energy requirement so that the batteries used often have to be replaced and on the other hand the device described in the specification has a substantial weight, which is a nuisance for the user, since the device should, to be properly used, be worn all the time. Another serious disadvantage lies in the size of the device specified which is about as long as a human hand and impairs the freedom of movement to the user. More particularly however the device in the above mentioned German patent specification is liable to attract attention owing to its size in the exposed position in which it is carried on the wrist and it will be a source of undesired curiosity on the part of strangers. Such an effect is more particularly undesirable, since the users are usually persons with cardiac complaints and convalescent persons, who must keep a watch on their cardiac activity and should not be exposed to any psychological strain.
Furthermore there has already been a proposal to provide a device for measuring the cardiac frequency which comprises a battery operated amplifier, accommodated in a box-shaped housing. Furthermore there are three stick-on electrodes, connected with the amplifier via separate cables, for producing an electrocardiogram and there is a wrist watch device, connected via three cables with the amplifier housing, for displaying the heart frequency measured by means of a suitable pointer-type display. Such a device however also suffers from a series of disadvantages, since it has an undesirably large number of individual components, which must be accommodated at different positions on the body and, respectively in the clothing and must be connected respectively with each other by means of three cables in each case. Furthermore the battery operated amplifier only runs for 72 hours with one battery charge and the spring driven watch device must be wound up every 24 hours. While the box comprising the current supply and the amplifier is to be carried with the computer and with the pulse generator in the pocket, the watch device, which only serves for indicating the cardiac frequency measured, has to be carried on the arm and furthermore does not have any safety devices which would provide an indication of a particularly low or particularly high cardiac frequency. Added to this one must consider that the large number of individual parts represents a nuisance for the patient and that the electrodes, which have to be connected via cables with the amplifier to be carried in the pocket have the tendency to detach themselves, since the cables are passed through articles of clothing to the amplifier.